Date   : Wed, 10 Apr 1985 16:42:38 GMT
From   : Dave Sweeney <dms%dciem.uucp@BRL-TGR.ARPA>
Subject: Re: Random Numbers

Nick Cuccia writes:
> 
> 
> function Random(var x: integer): real;
> 
> const
>   A = 2047;               (* = 2^11 - 1, a prime number *)
>   M = 524287;             (* = 2^19 - 1, a prime number *)
> 
> begin (* random *)
>     x := (A*x) mod M;             (* finding new seed value *)
>     Random := x / M;              (* finding next number in series *)
> end; (* function random *)

While A (= 2047) and M (= 524287) are mutually prime (HCF = 1), which
is all that is required for the algorithm, A is not a prime number:

       2047 = 23 * 89

which will hopefully discourage 16-bit-machine users from using it
for M (which must be prime for the series to have full period).
Here at DCIEM we use an implementation of the generator described
on p. 464 of Knuth's vol. 2, with k = 55, j = 31.  As no multiplications
or divisions are involved, it is reasonably fast.
-- 
       Dave Sweeney, DCIEM
       {allegra,ubc-vision,linus,ihnp4,uw-beaver,floyd}!utcsrgv!dciem!dms
or     {allegra,ihnp4,linus,decvax}!utzoo!dciem!dms